In certain electronic printed circuit board production situations, such as rework, repair, prototyping and research and development, it is often necessary to replace or exchange single components on populated printed circuit boards. Techniques for replacing components often involve applying solder paste, solder paste beads, solder tape or solder dots onto substrate pads on a circuit board for subsequent mounting of a new component onto the printed circuit board. In some instances, new solder is applied to existing solder on the printed circuit board on which a new component is mounted. The disadvantages of such single component placement techniques include placement inaccuracy, contamination, and inconsistent paste volume from pad to pad which can result in bridging problems and poor solder joints.
Prior art solutions to single component solder paste application techniques include the use of solder paste stencil printers such as those disclosed in U.S. Pat. Nos. 5,107,759 and 5,755,157, incorporated herein by reference. Such solder paste stencil printers are one-at-a-time, hand-operated stencil printers that provide a simple, accurate and consistent apparatus and method of stencil printing.
A variety of stencil patterns can be used with the hand-held stencil printer 10 shown in FIG. 1 by changing the stencil holder 17 that slips onto a mounting shaft 18 attached to the pivot arm assembly 11. As shown in FIG. 2, a stencil holder 21, as disclosed in U.S. Pat. No. 5,107,759 and U.S. Pat. No. 7,755,175, typically includes a cylindrical holder 22 and a stencil plate 23. The cylindrical holder 22 fits over the mounting shaft 18. The stencil plate 23 is disclosed as being permanently bonded to the cylindrical holder 22 to comprise the stencil holder 21. This is achieved by bonding the stencil plate 23 with adhesive to a conforming pad 25 that is bonded to a step washer 24 attached to the cylindrical holder 22. The conforming pad 25 and the step washer 24 each include a centrally-located aperture 27. Commercially available stencil holders as shown in FIG. 2 include stencil plates centrally-mounted to cylindrical holders, as described in U.S. Pat. No. 5,107,759, and flip-up stencil shovels side-mounted to cylindrical holders, as described in U.S. Pat. No. 5,704,287.
A variety of stencil patterns corresponding to a variety of circuit board patterns can be interchanged for use with the hand-held stencil printer 10. However, only a single stencil plate with a set configuration of apertures or footprint pattern can be used to print a specific solder pattern onto a printed circuit board. With the large number and variety of integrated circuits and electronic components available today, one must acquire a large number of stencil holders, one for each type of integrated circuit or electronic component to be soldered onto circuit boards. Therefore, a large number of stencil holders must be stocked in order to accommodate the large number and variety of stencil patterns required. Stencil holders, as shown in FIG. 2, are commercially available as single units, requiring the purchase of both the cylindrical holder 22 and the stencil plate 23 when only a change in stencil plate or pattern is required.